JOIN US"A suicide bomber driving a car packed with explosives drove into the minister's motorcade as he was driving out of a tunnel," the official told AFP, speaking on condition of anonymity.
He added that the minister survived the attack but 10 people travelling with him were wounded.
The attack came as Ali was heading to a hotel in Aden where he has been staying on a duty visit to the restive south.
Troops have been engaged in deadly fighting for months with al-Qaeda linked militants in Abyan province, east of the city.
Since May, the militants have taken control of three towns in Abyan, including its capital, Zinjibar, the scene of some of the fiercest fighting in recent months.
The government claims to have regained control of Zinjibar, but security officials have told AFP that the city remains partially under al-Qaeda's influence.
A witness told AFP that the explosion "was big and flames erupted from the bomb-laden car," adding that he saw wounded soldiers.
Today's assassination attempt was the second against Ahmad in less than a month.
On August 30, the minister escaped unharmed when a bomb targeting his convoy exploded near Al-Kud, a village in Abyan province the army had recaptured from al-Qaeda two days earlier.